The present invention relates to a radiotelephone system for making communications between one main unit and plural sub units.
Recently, using radio communication means instead of the curled cord for connecting the telephone main body and transmitter-receiver, various radiotelephone systems enhanced in portability and convenience are developed.
Hitherto, the radiotelephone system consisted of one main unit equivalent to the telephone main body in the wired telephone system, and one sub unit for making radio communications with the main unit, and made communications by using analog signals.
There are lately developed radiotelephone systems comprising a main unit and plural sub units, and having a radio transmission unit for sending and receiving the signals for controlling these two radiotelephone units by using digital signals. In such radiotelephone system, the main unit selects one out of the plural sub units, and sends signals to this sub unit for controlling, and after establishing the communication with the intended sub unit, one-to-one communication is made with this sub unit.
In such constitution, however, one main unit can communicate with only one sub unit at the same time, and point-to-multi-point (batch multiple address) communication such as notice from one main unit to all sub units was not possible.